Crop Sequences for Managing Cereal Cyst Nematode and Fungal Pathogens of Winter Wheat. RICHARD W. SMILEY, Professor, Oregon State University, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton 97801. RUSSELL E. INGHAM, Associate Professor, Oregon State University, Department of Botany and Plant Pathology, 2076 Cordley Hall, Corvallis 97331; WAKAR UDDIN, Former Faculty Research Assistant, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton 97801; and GORDON H. COOK, Field Crops Specialist, Union County Extension Service, 10507 North McAlister Road, La Grande, OR 97850. Plant Dis. 78:1142-1149. Accepted for publication 9 September 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1142.

In the Pacific Northwest, Heterodera avenae is spreading to soils infested with root-infecting fungal pathogens of wheat. A poorly drained, silty clay loam infested with multiple pathogens was used to examine productivity of winter wheat in 11 crop sequences. Breaks between wheat crops included summer fallow or crops of pea, barley, rape, alfalfa, or Kentucky bluegrass. In the fifth year, winter wheat was planted in all sequences, after one-half of each plot was treated with aldicarb. Yield of annual winter wheat was always 40-60% less than wheat alternated with fallow or any other crop, except alfalfa contaminated with grass weeds. Wheat yielded equally following 1- or 2-yr breaks from wheat. Effective breaks included summer fallow, pea, and weed-free alfalfa. H. avenae was the most important individual constraint to yield. Combined damage from H. avenae and Gaeumannomyces graminis var. tritici caused highest overall yield loss, whereas H. avenae and Pythium spp. had the greatest negative effect on number of roots. During the fifth year, where aldicarb was applied, root damage by H. avenae decreased but damage by Rhizoctonia solani and Pythium spp. increased, resulting in no yield improvement

Keyword(s): Brassica campestris, dryland root rot, Hordeum vulgare, Pisunt sativum, Poa pratensis, Pythium root rot, Rhizoctonia root rot, take-all, Temik, Triticum aestivum